Field of the Invention
The present invention relates to a method for manufacturing a sensor intermediate product having a sensor element for detecting the concentration of a gas to be detected, and to a method for manufacturing a sensor using the sensor intermediate product.
Description of Related Art
A known gas sensor for detecting the concentration of oxygen or NOx contained in exhaust gas discharged from an automobile or the like has a sensor element including a solid electrolyte member.
Such a gas sensor is known to have a structure in which a sensor element is inserted into a tubular metallic shell (housing) to be fixed to an exhaust pipe and is held such that its one end is exposed to a gas to be measured. In order to stably hold the sensor element inside the metallic shell and prevent entry of exhaust gas into the interior of the gas sensor, a holder for holding the sensor element, talc powder (filling member), a press member for pressing and compressing the talc powder, etc. are stacked, in this order from the forward end, within a space between the inner circumferential surface of the metallic shell and the outer circumferential surface of the sensor element. The sensor element is fixed inside the metallic shell as a result of the talc powder being compressed such that the talc powder is charged in the space between the metallic shell and the sensor element under pressure.
Incidentally, as shown in FIG. 5, compression of talc powder is performed as follows in a conventional gas sensor manufacturing method (see Patent Documents 1 and 2). First, a ceramic ring 300 and a second talc ring 226 are accommodated in a metal cup 20 with a sensor element 21 inserted therethrough (second disposing step), and the second talc ring 226 is compressed from the opening side of the metal cup 20 (second compression step). As a result, the second talc ring 226 is crushed and becomes powdery second talc 220, whereby an element unit 230 in which the sensor element 21 is held within the metal cup 20 and is united therewith is formed.
Next, the element unit 230 is inserted into a metallic shell 11 from the rear end side (the side toward a cylindrical portion for crimping 16) of a shell assembly 235, and a first talc ring 225, a sleeve 43, and a ring washer 45 are fitted onto the sensor element 21 from the side where the rear end 29 of the sensor element 21 is present (holding step). Subsequently, while the first talc ring 225 is being compressed, the cylindrical portion for crimping 16 is bent radially inward by means of heat crimping (first compression step), whereby a gas sensor is assembled.
Notably, in some cases, after the above-described first compression step, a protection sleeve (not shown) is fixed to the rear end of the metallic shell 11 by means of welding or the like, whereby a gas sensor is manufactured. Also, in some cases, after the sensor intermediate product having undergone the first compression step is made, this sensor intermediate product is transferred to a location for a different step, and the protection sleeve is then attached thereto so as to manufacture the gas sensor. Namely, the manufacturing process is divided into an intermediate step of manufacturing a sensor intermediate product and an assembly step of assembling the gas sensor for manufacture of the gas sensor.